Visual impairment: normal vision, low vision, legal or total blindness

Uveitis generally causes fluctuations in the vision of patients suffering from it, especially if it is recurrent or chronic. For many, it is a highly variable and unpredictable gray area: visual acuity decreases during active episodes of inflammation, but recovers with proper treatment. Occasionally, vision does not fully return, as the inflammation may leave sequelae that permanently affect certain delicate structures of the eyes. This occurrence will depend on many factors, such as some of the following: cause of the uveitis, anatomical location of the inflammation, severity of the inflammation, promptness of diagnosis, effectiveness of treatment and occurrence of complications. The progressive accumulation of all these factors leads to deterioration in patients' visual acuity and quality of vision.

Ocular complications associated with uveitis arise from two main factors: inflammation or side effects of treatments. Ocular inflammation can give rise to certain complications, especially when not controlled in time. These are more complex to remedy compared to those that may be caused by treatment side effects, mainly because they may already be present at the time of the initial ophthalmologic evaluation. Treatments for uveitis may also cause complications that affect vision but these can be prevented or remedied under periodic evaluation. The most common ocular complications that contribute to visual impairment are secondary glaucoma, secondary cataract, optic nerve atrophy, macular inflammation, retinal vascularization, vitreous opacification, epiretinal membrane formation, band keratopathy, among others. All of them can cause a decrease or changes in vision.

Uveitis is a disease that causes episodic visual impairment, but the recurrence of these episodes and the complications they trigger can cause permanent visual impairment. Visual impairments are classified in different ways, but in Puerto Rico and the United States they are described numerically and functionally as follows:

Normal vision

Normal vision is vision with visual acuity of 20/20, with or without correction.

Low vision or partial vision

Low vision is vision whose visual acuity is 20/70 or less for the best of the eyes, after all corrections; and/or which visual field is not greater than 30 degrees.

The term "low vision" can be used more arbitrarily to refer to visual impairment. It is a term that encompasses the spectrum of the myriad of visual fluctuations, from the mildest to the most severe. It is generally used to define visual impairment that interferes with the ability to perform daily activities and that CANNOT be corrected with the use of glasses. For this reason, it can be used to describe the experience of uveitis patients who experience visual fluctuations during episodes of inflammation and/or irreversible visual impairment.

Low vision patients still have enough vision to perform normal daily activities. However, they may present difficulties in perceiving textures, colors, transparencies, small details, faces, small letters, signs, etc. Everything will depend on the degree of severity of visual impairment.

Some patients can still drive during periods of ocular inflammatory inactivity, although it may be slightly more difficult at night and/or in unfamiliar places. Darkness and glare are two aspects that make night driving difficult.

During severe episodes of intermediate or posterior uveitis, patients experience a "temporary blindness" which in turn temporarily disables them from performing certain functions such as: driving, reading, writing, recognizing faces, etc. This may improve with treatment but, due to the delicacy of the eye structures, the sharpness of vision may be permanently affected. That is to say, patients may recover most of their vision, but may present some of the following problems: difficulty in perceiving different shades of colors and textures, discomfort and eyestrain, glare, etc.

Some irreversible complications of uveitis may cause sufficient visual impairment in some patients to meet the criteria for legal or total blindness. Likewise, a select group of uveitis cases have an aggressive and degenerative course. It is very important to recognize when these new visual needs arise in order to mobilize the rehabilitation process so that patients can acquire new skills to manage their vision loss.

Legal blindness

A person is considered legally blind when his or her visual acuity is 20/200 by the best of his or her eyes, after all corrections and/or whose field of vision is not greater than 20 degrees. In some cases, people with legal blindness can still perceive lights, silhouettes or large objects, but not enough to be guided by the sense of sight alone.

Total blindness

Total blindness manifests itself within a spectrum, but generally refers to a significant loss of vision in which the person can perceive neither light nor form.

Other vision changes related to uveitis

Visual acuity cannot be fully described with the Snellen visual acuity test. Although effective, it is a simple test that fails to represent the myriad of visual disturbances that anyone can experience, but especially uveitis patients. Often, some patients report that their vision has deteriorated, but their visual acuity still remains the same. In other words, the visual acuity test (Snellen) fails to represent the visual difficulties they experience in their daily lives. The universe is not monochromatic, like the Snellen test, but rather there is a great amalgam of colors, gradients, shades, textures, shadows, opacities, transparencies, depths, etc. Uveitis patients may present difficulties that affect their ability to perceive these factors that, together, determine visual sharpness. On the other hand, a phenomenon occurs in which the brain helps to create clearer images from ambiguous visual stimuli to compensate for the lack of visual acuity. For example, identifying letters whose typography is more particular and less ambiguous is easier than identifying those that are not. Letters such as "A, Z, X, S" are easier to distinguish than "O, G, Q, D, E, B". The brain compensates for those images that may not be as clear visually, but their stimulus is sufficient to get a general idea that is sometimes accurate. Because this set of factors cannot be measured by the visual acuity test, its result fails to represent the visual quality that patients experience on a daily basis.

Decreased or loss of contrast perception

It is usually caused by cataract formation and hinders the ability to distinguish colors and textures. Cataract can be surgically corrected. Other complications that may also hinder the perception of colors and textures are: retinal neovascularization and optic nerve inflammation.

Decreased or loss of the ability to detect depth (stereopsis)

Decreases the ability to perceive changes in depth.

Difficulty seeing in the dark (nyctalopia)

Uveitis can cause generalized difficulty seeing in the dark. Cataract formation can exacerbate this problem.

Decreased or loss of central vision

The loss of central vision associated with uveitis is usually caused by inflammation of the macula or optic nerve. It is usually perceived as a "void" in the center of vision. There are many other conditions of the macula that cause a decrease, alteration or loss of central vision. Some of them are macular degeneration, optic nerve atrophy or the formation of an epiretinal membrane.

Decreased or loss of peripheral vision

Decreased peripheral vision is usually caused by secondary glaucoma due to uveitis treatments.

Distortion or metamorphopsia

Distortion or metamorphopsia causes distortions in the field of vision, especially in the area of central vision. It may be more noticeable when focusing vision on straight lines. It is associated with inflammation of the macula, involvement of the optic nerve or formation of an epiretinal membrane.

Ocular problems related to uveitis

Photophobia

Photophobia causes eye pain when patients are in brightly lit places. It occurs in cases of anterior uveitis with ocular synechiae, a condition in which the iris sticks to the cornea (anterior) or lens (posterior). This causes extremely severe pain in the presence of even the slightest illumination. Even after periods of ocular inflammation, the eyes may remain sensitive to intense light. It may also occur as a side effect of treatments, especially topical or local ones.

Glare

It is a phenomenon that affects everyone, but uveitis patients may be more sensitive to it. It occurs when we observe intense lights such as flashes, flashes, automobile lights and their reflections in the mirror, etc. It also happens when we go out during the day and the sunlight is very intense. It produces discomfort and difficulty to observe, especially when what we want to see is backlit.

Flashes of light or photopsia

Photopsias or flashes of light may appear unexpectedly. They usually occur when we close our eyes or we are exposed to a lot of light intensity. In addition, they can also occur prior to retinal detachment, in people suffering from migraine or when the optic nerve is inflamed.

Fatigue or eye discomfort

Everyone experiences eye strain or discomfort at some point. It usually happens after extensive reading or looking at the screens of electronic devices. However, uveitis patients experience eye strain or discomfort more frequently, even when there are no active episodes of inflammation. This impacts the amount of time they can spend reading, studying or working because they need to take visual breaks more often.

None of the visual changes mentioned are refractive problems. That is, they cannot be corrected with the use of lenses. Refractive problems include: myopia, astigmatism, hyperopia, hyperopia. These can be corrected with the help of an optometrist.

Individuals and uveitis patients who experience visual impairments that hinder their lifestyle may benefit from an evaluation by a low vision optometrist or vision rehabilitation services. This may help them acquire tools and skills to manage vision impairment or loss.

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